Coating technologies are used broadly to tune the surface characteristics of solid substrates. Polymer coatings are routinely used for biocompatibilization, targeted and controlled release of therapeutics, the synthesis of hollow capsules via template-core etching, and stabilizing dispersions. For example, coatings are applied to protect surfaces from environmental damage or biofouling, alter surface hydrophobicity, make the solid biocompatible, enable covalent modification, or protect against particle aggregation. Covalently grafted polymers on solid supports have certain advantages over physisorbed coatings. Covalently grafted polymer coatings can be more stable at high solids concentrations than physisorbed coatings. They are also not susceptible to bridging or depletion flocculation. Covalently grafted polymers can also be more hydrolytically stable. Synthetic strategies for grafting polymer coatings on solid supports include suspension, dispersion, or emulsion polymerizations, grafting-to strategies, surface-initiated polymerization, as well as layer-by-layer assembly followed by chemical crosslinking While these synthetic approaches are quite versatile, they possess certain drawbacks that are exemplified by not meeting the low-cost requirements for coating commodity chemicals, such as the titanium dioxide (TiO2) pigment used in paints. Grafting-to approaches frequently lead to low surface coverages and therefore might not provide appropriate coating properties. Grafting-from approaches require the covalent attachment and removal of a polymerization catalyst or chain-transfer agent in order to avoid homopolymerization. Layer-by-Layer synthesis is a multiple-pot process. Suspension, dispersion, and emulsion polymerizations tend to have low-yields of solids in each solution, particularly for less than 100 nm thick coatings. Thus, the prevailing syntheses often require multiple steps and/or low yield syntheses, and result in low surface coverage and/or non-uniform coatings on the nanoscale. As TiO2 and other commodity chemicals require high yield, low cost coating syntheses, an alternative to these multiple step, multiple pot, and low yield approaches would be useful.
Moreover, uniform nanoscale coatings that mitigate the aggregation of inorganic-oxide particles can be invaluable in dispersion applications. In point, the inorganic-oxide particle pigment is often used in large excess due to it aggregation in order to maintain appropriate hiding. As TiO2 is the most energy demanding ingredient in paint products, enhanced dispersion stability is a pressing sustainability issue.
TiO2 is the optimal white pigment for paint due to its significant hiding capacity, stability, low toxicity, and relatively low cost. Agglomeration of TiO2 reduces hiding, requiring the addition of excess pigment in paint formulations to achieve similar optical properties, a significant source of waste in the paint industry. Non-covalent coatings such as surfactants and polyelectrolytes enhance the stability of TiO2 dispersions through steric and/or electrostatic effects. However, non-covalent coatings are prone to bridging and depletion flocculation, particularly at high concentrations. Covalent coatings with high surface coverage, thicknesses of many nanometers, flexibility, and charge have empirically been shown to enhance particle dispersion. The synthetic approaches for grafting polymers on solid supports listed above unfortunately can yield insufficient polymer surface coverage or charge per surface area for stable dispersions, can be unable to obtain coating thicknesses of roughly 5-75 nm, and can have prohibitively high cost.
Providing a more efficient synthesis for an improved polymer coated oxide particle would be of great value to the industry.